Both athletes have urged other athletes not to take sporting supplements, and Brownlee, who won gold at London 2012 and Glasgow 2014, feels it is important to take extra care.

"What you can do is be careful on the high-risk things," he added.

"For example, if I know that an energy supplement is made in the same factory as a cough medicine, I know the potential for contamination is much, much higher. You have to be more careful about those and use the ones that are batch-tested."